Principles of Agricultural Science – Plant

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The Size of the Matter

Unit 2 – Mineral SoilsLesson 2.1 Understanding Soil Properties

Principles of Agricultural Science – Plant

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The Components

Soils have four main components that make up the whole

Minerals, 45%

Organic Matter, 5%

Air, 25%

Water, 25%

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10%

20%

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100%

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Soil Parts

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Soil Particles

There are three main sizes of soil particles:

• Sand

• Silt

• Clay

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Sand

• .05 – 2 mm

• Round shape

• Feels gritty

Attributes to Soil

• Adds porosity

• Reduces water holding capacity

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Silt

• .002 - .05 mm

• Round shape – but very small to detect

• Feel smooth but does not stick together very well

Attributes to Soil

• Moderately good for porosity

• Helps water holding capacity

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Clay

• Less than .002 mm• Flat or platy• Sticky when wet – ribbon test

• Bad for porosity• Ties up water so plants can’t use it

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Relative Size of Particles

Sand Silt Clay

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Testing for Particles

Field tests can be done to determine the presence of each particle:

1. Moisten a sample of soil with water in your hand.

2. Break up all clods and add enough water to make a slurry.

3. Rub a thin layer of slurry between your thumb and forefinger to isolate the particles.

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Detection of Particles

• Sand is relatively easy to detect the gritty particles

• Wet silts may seem slick like clay but not sticky

• Conduct a ribbon test to determine how much clay content is present

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The Textural Triangle

The triangle helps you determine

classifications for soil

textures

Huddleston & Kling, 1996

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Loams

Loam that has less than 27% clay is a mixture of sand, silt, and clay.

Loam soils are considered to be the optimal soils for growing plants.

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References

Huddleston, J. H., & Kling, G. F. (1996). Manual for judging Oregon soils. Corvallis, OR: Oregon State University.

Parker, R. (2010). Plant and soil science: Fundamentals and applications. Clifton Park, NY: Delmar.

Plaster, E. J. (2003). Soil science & management (4th ed.). Clifton Park, NY: Delmar.